1. Field of the Invention
This invention relates to hose, and more particularly relates to hose having improved axial strength. The invention is especially concerned with hose which can be used in cryogenic conditions.
2. Description of the Related Art
Typical applications for hose involve the pumping of fluids from a fluid reservoir under pressure. Examples include supplying of domestic heating oil or LPG to a boiler; transporting produced oilfield liquids and/or gases from a fixed or floating production platform to the cargo hold of a ship, or from a ship cargo hold to a land-based storage unit; delivering of fuel to racing cars, especially during refuelling in formula 1; and conveying corrosive fluids, such as sulphuric acid.
It is well known to use hose for the transport of fluids, such as liquefied gases, at low temperature. Such hose is commonly used to transport liquefied gases such as liquefied natural gas (LNG) and liquefied propane gas (LPG).
In order for the hose to be sufficiently flexible, any given length must be at least partially constructed of flexible materials, i.e., non-rigid materials.
The structure of such hose generally comprises a tubular body of flexible material arranged between the inner and outer helically wound retaining wires. It is conventional for the two wires to be wound at the same pitch, but to have the windings displaced by half a pitch width from one another. The tubular body typically comprises inner and outer layers with an intermediate sealing layer. The inner and outer layers provide the structure with the strength to carry the fluid therein. Conventionally, the inner and outer layers of the tubular body comprise fabric layers formed of a polyester such as polyethylene terephthalate. The intermediate sealing layer provides a seal to prevent the fluid from penetrating the hose, and is typically a polymeric film.
The retaining wires are typically applied under tension around the inside and outside surfaces of the tubular body. The retaining wires act primarily to preserve the geometry of the tubular body. Furthermore, the outer wire may act to restrain excessive hoop deformation of the hose under high pressure. The inner and outer wires may also act to resist crushing of the hose.
A hose of this general type is described in European patent publication no. 0076540A1. The hose described in this specification includes an intermediate layer of biaxially oriented polypropylene, which is said to improve the ability of the hose to resist the fatigue caused by repeated flexing.
Another hose is described in GB-2223817A. The hose described in this publication is a composite hose comprising an inner helical metallic core, a plurality of layers of plastics material fibres and films wound on the core, at least one layer of glass cloth and at least one layer of aluminium foil disposed adjacent one another and wound onto the plastics material, and an outer helical metallic former. This hose is said to be suitable for transporting flammable fuels and oils. Various improvements to composite hose are described in our WO01/96772, WO 2004/044472 and WO 2004/079248, the contents of which are incorporated by reference.
Another hose structure is disclosed in U.S. Pat. No. 3,856,052.
Broadly, we provide an axial strengthening means for hose, whereby the hose can withstand greater axial tension than has previously been possible, without impairing the other properties of the hose.